1. Technical Field
The present invention relates to a semiconductor device performing signal transmission between a first semiconductor chip and a second semiconductor chip using induction coupling of inductors, a method of manufacturing the semiconductor device, and a lead frame thereof.
2. Related Art
When signals are transmitted between two semiconductor chips which are not in contact, there are many cases of using a photo-coupler (e.g., Japanese Laid-open patent publication NO. 2004-186297). However, since the photo-coupler has a light emitting element and a light receiving element, it is difficult to reduce the photo-coupler in size. When a frequency of an electric signal is high, it is difficult to follow the electric signal.
Hereupon, recently, as described in Japanese Laid-open patent publication NOS. 2009-49035 and 2007-165459, a technique has been developed in which two inductors are provided between two semiconductor chips, and signals are transmitted and received between the inductors, thereby transmitting the signals between the two semiconductor chips which are not in contact.
In the technique described in Japanese Laid-open patent publication NO. 2009-49035, an insulating transformer formed by superposing a second semiconductor substrate having a second inductor over a first semiconductor substrate having a first inductor is provided between a first semiconductor chip and a second semiconductor chip. As for the insulating transformer, surfaces of the first semiconductor substrate and the second semiconductor substrate may be overlapped to each other in the opposed direction. One semiconductor substrate is provided with a through-hole for drawing out an interconnect connected to the inductor toward the rear side.
In the technique described in Japanese Laid-open patent publication NO. 2007-165459, a first inductor is formed in an interconnect layer of a first semiconductor chip, a second inductor is formed in an interconnect layer of a second semiconductor chip, and the inductors of the first semiconductor chip and the second semiconductor chip are overlapped to be opposed to each other.
In Japanese Laid-open patent publication NO. 2007-123650, it is disclosed that a first semiconductor chip having a first inductor and a second semiconductor chip having a second inductor are independently mounted over different lead frames, and the two semiconductor chips are opposed with a gap.
In order to raise a coupling coefficient between inductors, it is preferable that semiconductor chips or semiconductor substrates are overlapped in a direction in which interconnect layers are opposed to each other, thereby preventing the semiconductor substrate from being positioned between the inductors as described in Japanese Laid-open patent publication NOS. 2009-49035 and 2007-165459. However, with such a configuration, it is necessary to provide external connection terminals of the semiconductor device on the rear side of the substrate. In this case, for example, as described in Japanese Laid-open patent publication NO. 2004-186297, it is necessary to provide the semiconductor substrate with the through-hole. When the semiconductor substrate is provided with the through-hole, the manufacturing cost of the semiconductor device is increased.
In the technique described in Japanese Laid-open Patent publication NO. 2007-123650, it is necessary to broaden the gap between two semiconductor chips to connect a lead frame to the semiconductor chip by a wire. In this case, a coupling coefficient between the inductors becomes low.
As described above, it is difficult to raise the coupling coefficient between inductors while decreasing the manufacturing cost of the semiconductor device.